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FLKook
Joined: 28 Apr 2001
Posts: 710
Location: East Central Florida |
 Thu Mar 07, 2002 12:35 am
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Here is 3T3's FE image grab 24 hours later. She made a comment about not wanting to be an air traffic controller, I'm inclined to agree!! SDCADJ, give us today's report (03/06) when you check in.
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SDCADJ
Joined: 14 Nov 2001
Posts: 65
Location: San Diego, CA USA |
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Thu Mar 07, 2002 2:28 am
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Hey guys.. Thanks for another screen shot. Unfortunately, I couldn't corelate with yesterdays activity because we are completely covered in clouds today (it's supposed to rain!)...
From what I can tell, we've got white out today, and then we have low clouds under the white out.. Would it make sense that the white out that the trails cause would be ABOVE the normal clouds?
I also did see some chemtrails under the white out too though, so it's all just plain wierdness in the sky today.
LAX is sure a busy airport isn't it? They also have 3 other airports around it, so that's why folks who live in LA would never be able to use Flight explorer there are just too many plains, although I'm sure FE let's you zoom in on your specific area doesn't it?
Anyway, I got a reply from Dr. Minnis. I will post it in my next message.
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SDCADJ
Joined: 14 Nov 2001
Posts: 65
Location: San Diego, CA USA |
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Thu Mar 07, 2002 2:29 am
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Dear Mr. -----,
Thanks for your interest and your comments on the contrail forecast
analysis on the web. You may be sorry that you wrote me because I tend to
get a bit wordy. I did not find any attachment to the email, so I am not
certain which hour and set of conditions you were viewing on the contrail
forecast site. Please remember that the time given on each image is UTC
(Universal Coordinated Time or GMT or Zulu) and the local time in
California is 8 hours earlier, so you need to subtract 8 hours from time
on each picture, e.g., 1800 UTC = 1000 AM PST.
As stated in the comments on the web site, the predictions are not 100%
accurate for a variety of reasons. Contrails are especially difficult to
predict over the west coast because all of your weather comes from the
Pacific where there no balloon sounding stations.
Nevertheless, if I go to the old contrail predictor and select efficiency =
0.4 and ask for a 12 image sequence, I get the first hour starting at 1100
UTC when most people are sleeping and it ends at 2100 UTC (100 PM). Hours
1200 and 1700 are missing. By the time you get this, you will be looking at
a different start time. You can reproduce this sequence by accessing the
archive starting at 11 GMT, date = 20010305. I will describe what I see.
Please keep in mind that a person at the surface will be able to see
contrails that are more than 150 miles when thet are at 35,000 feet. Here
is I what I see:
1100 UTC (3:00 AM PST) Contrails just north of SDbetween 250 and 300 mb.
1300 UTC (4:00 AM) Contrails directly over SD (250-300 mb)
1400 UTC (6:00 AM) Ditto (225-300 MB)
1500 UTC (7:00 AM) Contrails just west of SD at 200 Mb, to the east at 275 mb
1600 UTC (8:00 AM) Contrails just west of SD at 175-225 mb
1800 UTC (10:00 AM) Contrails on the coast of SD 175-225 mb
1900 UTC (11:00 AM) No contrails
2000 UTC (12:00 AM) No contrails
2100 UTC (1:00 PM) contrails to north and west of SD
What that tells me is that the weather diagnostic model used to determine
the potential for contrails was not doing too bad of a job for today.
However, as your mail was dated 1235 PM (I assume PST) then you have been
seeing contrails all morning and the forecaster suddenly turns off the
contrails at 11:00 AM. If you are seeing contrails, then the model is not
doing too well at 11 and 12 AM. Because this web site is being used for
research to develop an accurate contrail forecaster, we expect to see
errors like this. That is why we added in another feature.
As you can surmise, the contrails were generally occurring between 175 and
250 mb. If we select our other option, "Individual level (mb) at 0.3
efficiency", and select 225 mb and 12 hours, you see a different kind of
plot. This time you only see what is happening at 225 mb. The little
circles correspond to a relative humidity (with respect to ice, RHI) range
(green is 70-85%; yellow is 85 - 00%, orange is 100 - 115%, etc.) and the
x's are the locations for contrails. The reason we plot the relative
humidity levels is that the humidity at high altitudes is usually measured
too low by the weather service balloons. Since those balloon soundings are
used in the models, we often have areas that are too dry. Now if you go
back to the hours that showed no contrails you will see the following:
1900 UTC Yellow & green circles surrounding SD
2000 UTC green around SD
2100 UTC green around SD
Thus, the modeled relative humidity is somewhere around 80-85%. We know
from previous studies that natural cirrus clouds typically form when the
actual (not the ballon-measured or modeled value) relative humidity is
above 135%. Contrails persist and spread into cirrus clouds if the
relative humidity is above 100%. Previous studies suggest that, at
altitudes corresponding to 225 mb (37,000 ft), the balloon sounding is
often to0 dry by about 35%. Thus, the true humidity at 225 mb is probably
closer to 80 + 35 = 115%, a value that, if true, will produce plenty of
spreading contrails if aircraft are flying at that altitude.
The problem we face is determining some means to accurately account for the
dry bias in the soundings and then to inform the weather modelers what we
have found and that they shoudl try to correct for it. If that ever
happens, then we can have mor eaccurate contrail forecasts. Or, we may come
up with our own fix and apply it to the model data when we make our
contrail predictions.
In reading the above discussion, I hope you can appreciate the problem a
little more and understand that we cannot claim to nail every potential
contrail occurrence. Our goal is to improve the forecast and hopefully,
through interactions with the weather modelers, improve their weather
forecasts.
Sincerely,
Patrick Minnis
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